H-bridge motor driving circuit

ABSTRACT

An H-bridge motor driving circuit has, between a PWM comparator and a control circuit, first and second frequency dividers for frequency-dividing, by 2, an AND gate, OR gate, and first and second and second inverters. During a first period, the first and second MOS transistors are turned on, and the second and third MOS transistors are turned off, caused a current to flow through a motor. During a next second period, the third and fourth MOS transistors are turned on, and the first and second MOS transistors are turned off, causing a regenerative current to flow through the motor. During a next third period, the MOS transistors are turned on and off in the same manner as during the first period, causing a current to flow through the motor. During a final fourth period, the first and second MOS transistors are turned on, and the third and fourth MOS transistors are turned off, caused a regenerative current to flow through the motor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an H-bridge motor driving circuit forcontrolling a DC motor using pulse width modulation (PWM).

2. Description of the Related Art

One general motor driving circuit for controlling a DC motor to rotateselectively in normal and reverse directions is an H-bridge motordriving circuit which has an H-shaped bridge circuit comprising fourtransistors and a DC motor. The four transistors are turned on and offto energize, de-energize, and rotate the DC motor selectively in thenormal and reverse directions.

FIG. 1 of the accompanying drawings shows a typical conventionalH-bridge motor driving circuit.

As shown in FIG. 1, the conventional H-bridge motor driving circuitcomprises H-bridge output circuit 10, triangular wave oscillator 11, PWMcomparator 12, inverter 13, and control circuit 14.

H-bridge output circuit 10 has MOS transistors Q₁, Q₂ each having adrain connected to the positive terminal of a DC power supply E, asource connected to the circuit board, and a gate supplied with controlsignals S₁₁, S₁₂, respectively, for turning on and off MOS transistorsQ₁, Q₂, and MOS transistors Q₃, Q₄, each having a drain connected to thesources of MOS transistors Q₁, Q₂, respectively, a source connected tothe circuit boards and a ground potential point to which the negativeterminal of the DC power supply E is connected, and a gate supplied withcontrol signals S₁₃, S₁₄, respectively, for turning on and off MOStransistors Q₃, Q₄. Motor M is connected between the junction betweenMOS transistors Q₁, Q₃ and the junction between MOS transistors Q₂, Q₄.Parasitic diodes D₁ through D₄ exist at the junctions between thesources of MOS transistors Q₁ through Q₄, the circuit board, and thedrains of MOS transistors Q₁ through Q₄.

Triangular wave oscillator 11 generates triangular wave signal S₂₁.

PWM comparator 12 compares triangular wave signal S₂₁ from triangularwave oscillator 11 with constant-level signal S₂₂, and outputs PWM pulsesignal S₂₃.

Inverter 13 inverts pulse signal S₂₃ from PWM comparator 12 into pulsesignal S₂₄.

Control circuit 14 is supplied with pulse signals S₂₃, S₂₄,power-supply-level signals S₂₅, S₂₆, and rotation control signal S₀, andoutputs signals S₂₅, S₂₄, S₂₆, S₂₃ as control signals S₁₁ through S₁₄for MOS transistors Q₁ through Q₄.

Operation of the conventional H-bridge motor driving circuit shown inFIG. 1 will be described below with reference to a timing chart of FIG.4 of the accompanying drawings.

Triangular wave signal S₂₁ generated by triangular wave oscillator 11and constant-level signal S₂₂ are supplied to comparator 12, whichgenerates PWM pulse signal S₂₃. PWM pulse signal S₂₃ is inverted intosignal S₂₄ by inverter 13. Signals S₂₃, S₂₄, power-supply-level signalS₂₅. and ground-level signal S₂₆ are supplied to control circuit 14, andthen applied as respective control signals S₁₄, S₁₂, S₁₁, S₁₃ to thegates of MOS transistors Q₄, Q₂, Q₁, Q₃, respectively. It is assumedthat MOS transistors Q₁, Q₄ are energized , and MOS transistor Q₄ isPWM-controlled. During period T₁, signals S₂₃, S₂₅ are high and MOStransistors Q₁, Q₄ are turned on, causing a current to flow throughmotor M. During period T₂, signals S₂₄, S₂₅ are high and MOS transistorsQ₁, Q₂ are turned on, entering a regenerative mode to produce aregenerative current flowing through a loop from motor M to MOStransistor Q₂ to MOS transistor Q₁ to motor M (in case of an inductiveload). In case of a resistive load, the MOS transistors are notconducted.

The conventional H-bridge motor driving circuit described above isdisadvantageous in that since MOS transistor Q₁ is energized at alltimes and hence a current flows through MOS transistor Q₁ at all times,a large amount of electric power needs to be supplied to the H-bridgemotor driving circuit, which generates a large amount of heat and hencesuffers poor reliability. The H-bridge motor driving circuit isnecessarily of increased cost as it needs a high-performance device suchas a low-on-resistance MOSFET or a low-saturation-voltage transistor forreducing the amount of generated heat.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an H-bridge motordriving circuit which includes a circuit arrangement for distributing anamount of applied electric power among a plurality of transistors toequalize the amounts of heat generated by the transistors.

To achieve the above object, an H-bridge motor driving circuit accordingto the present invention comprises, connected between a PWM comparatorand a control circuit, first and second frequency dividers forfrequency-dividing, by 2, an output signal from the PWM comparator withpositive-going edges and negative-going edges, respectively, thereof, anAND gate for ANDing an output signal from the first frequency divider,an OR gate for ORing the output signal from the first frequency dividerand the output signal from the second frequency divider, and first andsecond inverters for inverting an output signal from the AND gate and anoutput signal from the OR gate, respectively.

The control circuit applies an output signal from the first inverter, anoutput signal from the second inverter, the output signal from the ANDgate, and the output signal from the OR gate to the gates of first,second, third, and fourth MOS transistors, respectively.

During a first period, the first and second transistors are turned on,and the second and third transistors are turned off, causing a currentto flow through a motor. During a next second period, the third andfourth transistors are turned on, and the first and second transistorsare turned off, causing a regenerative current to flow through themotor. During a next third period, the MOS transistors are turned on andoff in the same manner as during the first period, causing a current toflow through the motor. During a final fourth period, the first andsecond transistors are turned on, and the third and fourth transistorsare turned off, causing a regenerative current to flow through themotor.

In a regenerative mode, the first and second MOS transistors, and thethird and fourth MOS transistors are alternately turned on. Therefore,the amount of applied electric power is distributed among the MOStransistors, thus equalizing the amounts of heat generated by the MOStransistors.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description withreference t the accompanying drawing s which illustrate an example ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a conventional H-bridge motor drivingcircuit;

FIG. 2 is a diagram showing waveforms in various portions of theconventional H-bridge motor driving circuit shown in FIG. 1;

FIG. 3 is a circuit diagram of an H-bridge motor driving circuitaccording to the present invention; and

FIG. 4 is a diagram showing waveforms in various portions of theH-bridge motor driving circuit shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 3, an H-bridge motor driving circuit according to anembodiment of the present invention comprises triangular wave oscillator1, PWM comparator 2 for comparing triangular wave signal S₁ and an inputsignal S₂ with each other, frequency dividers 3, 4 forfrequency-dividing, by 2, output signal S₃ from PWM comparator 2 withpositive-going edges and negative-going edges, respectively, thereof,AND gate 5 and OR gate 6 for ANDing and ORing, respectively, outputsignals S₄, S₅ from frequency dividers 3, 4, inverters 7, 8 forinverting output signals S₆, S₈, respectively, from AND gate 5 and ORgate 6 into respective signals S₇, S₉, H-bridge output circuit 10, andcontrol circuit 9 for outputting control signals S₁₁, S₁₂, S₁₃, S₁₄ fromsignals S₆, S₇, S₈, S₉ and rotation control signal S₀ indicative ofwhether motor M spins in a normal or reverse direction, to turn on andoff MOS transistors Q₁, Q₂, Q₃, Q₄. H-bridge output circuit 10 is of anarrangement identical to the arrangement of H-bridge output circuit 10of the conventional H-bridge motor driving circuit shown in FIG. 1.

Operation of the H-bridge motor driving circuit according to the presentembodiment will be described below with reference to FIG. 4. FIG. 4shows waveforms in various portions of the H-bridge motor drivingcircuit at the time motor M rotates in the normal direction. When motorM rotates in the reverse direction, signals S₁₃, S₁₁ and signals S₁₄,S₁₂ are switched around.

Triangular wave signal S₁ generated by triangular wave oscillator 1 andinput signal S₂ are supplied to PWM comparator 2, which generates PWMpulse signal S₃. Frequency dividers 3, 4 frequency-divide, by 2, PWMpulse signal S₃ from PWM comparator 2 with positive-going edges andnegative-going edges, respectively, thereof. Specifically, frequencydivider 3 frequency-divides PWM pulse signal S₃ with positive-goingedges thereof, producing pulse signal S₄, and frequency divider 4frequency-divides PWM pulse signal S₃ with negative-going edges thereof,producing pulse signal S₅. These pulse signals S₄, S₅ have the samefrequency as the frequency of triangular wave signal S₁ output fromtriangular wave oscillator 1, and are shifted out of phase withtriangular wave signal S₁ by the period of the high level of PWM pulsesignal S₃. Pulse signals S₄, S₅ output from frequency dividers 3, 4 areapplied to AND gate 5 and OR gate 6, respectively, which generate pulsesignals S₆, S₈, respectively. Pulse signals S₆, S₈ are then inverted byrespective inverters 7, 8 into inverted pulse signals S₇, S₉. Pulsesignals S₆, S₇, S₈, S₉ are supplied to control circuit 9, which applythem as control signals S₁₃, S₁₁, S₁₄, S₁₂ to the gates of MOStransistors Q₃, Q₁, Q₄, Q₂, respectively.

It is assumed that MOS transistors Q₁, Q₄ are energized. With theconventional H-bridge motor driving circuit, only MOS transistor Q₁ oronly the MOS transistor Q₄ is switched to drive motor M according toPWM. According to the present invention, MOS transistors Q₁, Q₄ arealternatively switched to drive motor M according to PWM. Pulse signalS₇ is applied as the gate signal S₁₁ for MOS transistor Q₁, pulse signalS₉ is applied as the gate signal S₁₂ for MOS transistor Q₂, pulse signalS₆ is applied as the gate signal S₁₃ for MOS transistor Q₃, and pulsesignal S₈ is applied as the gate signal S₁₄ for MOS transistor Q₄. Onesequence of operating patterns of MOS transistors Q₃, Q₁, Q₄, Q₂ isindicated in periods T₁ through T₄. States of signals and MOStransistors in each of periods T₁ through T₄ will be described below.

During period T₁, pulse signals S₇, S₈ are high. As a result, MOStransistors Q₁, Q₄ are turned on, and MOS transistors Q₂, Q₃ are turnedoff, causing a current to flow through motor M.

During period T₂, pulse signals S₆, S₈ are high. As a result, MOStransistors Q₃, Q₄ are turned on, and MOS transistors Q₁, Q₂ are turnedoff. At this time, H-bridge output circuit 10 enters a regenerative modeto produce a regenerative current flowing through a loop from motor M toMOS transistor Q₄ to MOS transistor Q₃ to motor M (in case of aninductive load). In case of a resistive load, the MOS transistors arenot conducted.

During period T₃, pulse signals S₇, S₈ are high. As a result, MOStransistors Q₁, Q₂ are turned on, and MOS transistors Q₃, Q₄ are turnedoff. At this time, H-bridge output circuit 10 enters the regenerativemode to produce a regenerative current flowing through a loop from motorM to MOS transistor Q₂ to MOS transistor Q₁ to motor M (in case of aninductive load). In case of a resistive load, the MOS transistors arenot conducted.

While a preferred embodiment of the present invention has been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

What is claimed is:
 1. An H-bridge motor driving circuit comprising: anH-bridge output circuit for driving a motor, said H-bridge outputcircuit including first and second MOS transistors having sources anddrains, either of which are connected to a first terminal of a DC powersupply, parasitic diodes existing between the sources and the drains andto which a voltage of the DC power supply is applicable in a reversedirection, and gates for being supplied with control signals to controlconduction/non-conduction of the first and second MOS transistors, andthird and fourth MOS transistors having sources and drains, either ofwhich are connected to the other of the sources and the drains of saidfirst and second MOS transistors and others of which are connected to asecond terminal of the DC power supply, parasitic diodes existingbetween the sources and the drains and to which the voltage of the DCpower supply is applicable in a reverse direction, and gates for beingsupplied with control signals to control conduction/non-conduction ofthe third and fourth MOS transistors, said motor being connected betweena junction between said first and third MOS transistors and a junctionbetween said second and fourth transistors; a triangular wave oscillatorfor generating a triangular wave signal; a PWM comparator for comparingsaid triangular wave signal with a constant-level signal; first andsecond frequency dividers, each frequency-dividing, by 2, an outputsignal from said PWM comparator with positive-going edges andnegative-going edges, respectively, thereof; an AND gate for ANDing anoutput signal from said first frequency divider and an output signalfrom said second frequency divider; an OR gate for ORing the outputsignal from said first frequency divider and the output signal from saidsecond frequency divider; first and second inverters, each inverting anoutput signal from said AND gate and an output signal from said OR gate,respectively; and a control circuit for applying an output signal fromsaid first inverter, an output signal from said second inverter, theoutput signal from said AND gate, and the output signal from said ORgate to the gates of the first, second, third, and fourth MOStransistors, respectively.